1. Field of the Invention
This invention relates to a monolithic or laminated glazing for motor vehicles, exhibiting at least one filtering zone for attenuating light radiation and heat radiation.
2. Background of the Related Art
Glazings, and in particular windshields having at least one filtering zone, for example a filtering band in the upper part, are known in various forms.
Laminated windshields generally consist of two glass sheets and an inserted thermoplastic sheet of polyvinyl butyral, tinted in its upper part with organic coloring agents. One of the drawbacks of this type of windshield is that the organic coloring agents have a low light resistance, so that the tinted areas of the polyvinyl butyral sheet fade in time under the effect of the light.
In the case of another type of known windshield, as described, for example, in DE-OS 1 596 919, the glass sheet constituting the glazing is provided with a filtering layer with a metal oxide base, the production of this filtering layer being performed by application on the glazing of a solution of inorganic metal compounds which are oxidized into coloring metal oxides at higher temperatures. The solution containing the metal compounds is sprayed on the surface of the glass and pyrolysis takes place during a subsequent heat treatment. The spraying process makes it possible to apply only with difficulty a thin and uniform layer in a reproducible manner, so that this process is not suitable for an industrial production.
Other known windshields, for example that disclosed in DE-OS 1 951 616, use a filtering band made with an inorganic bakable enamel which is printed by silk-screening on the surface of the glass and which then is baked. The bakable enamel in this case consists of a glass with a low melting point and of colored pigments of metal oxides dispersed in the glass. The bakable enamel can have a transparency of 0 to 40%. The bakable enamel is printed according to such a screen that the transmission of the light gradually increases from the edge up to the zone of vision. Such filtering bands with a bakable enamel base of the glaze type also exhibit various drawbacks. The bakable enamels of the glaze type always have, for example, a certain characteristic cloudiness and form a rough surface, so that they do not make it possible to obtain clear transparent layers. Moreover, it is known that the solidity of the glass is reduced by the layers of the glaze type, which proves troublesome since the filtering bands cover a relatively large surface of the glazing.